Focus Fusion Safety

In the course of online discussion coming from our crowdfunding campaigns, some wildly inaccurate claims have been made by others about the production of radioactive waste in a Focus Fusion generator. We’ve replied online, but it is important to set the record straight in a document available on our own website, which we are doing here.

First, LPPFusion has always said that a Focus Fusion generator would produce no “radioactive waste” NOT “no radioactivity.” Just about everything has some radioactivity—including human beings. But radioactive waste has radioactivity at dangerous levels. For example Class A waste, the least dangerous, has a radioactive level of 3.5 microcuries/cc.

While the main reaction in a pB11 generator is aneutronic, meaning it produces no neutrons, there are secondary reactions that produce about one neutron for every 200 aneutronic reactions. This neutron can produce tiny amounts of radioactivity in pure beryllium electrodes in two ways. First, about one in every 24,000 neutrons will be absorbed by a Be9 nucleus to create Be10, a radioactive isotope. After a month in a generator (about as long as we think the electrodes can last before they are eroded out of shape) the electrodes will have about 1 nanocurie/cc from this source which is 3,000 times less than the least radioactive waste.

Second, about 1 in 400 neutrons will break apart the Be9 nucleus, forming Li6 and He4. Neither of these is radioactive, but in a month’s time, about one in 26,000 Li6 nuclei will absorb a neutron, producing another He4 nucleus and a tritium nucleus. Tritium is a radioactive isotope of hydrogen, with a 12.6 year half-life. At the 800 °C temperatures of the electrodes in the generator, the tritium will almost all escape into the chamber or the cooling helium gas. The tritium within the chamber will eventually be exhausted with the product of the main pB11 reaction, which is also helium.

If the tritium produced by a single 5MW Focus Fusion generator is simply diluted by a flow of 1,000 gallons a day of water (less than three U.S. households’ use) the amount of radioactivity will be below U.S. safety limits for drinking water. The tiny amount of tritium trapped inside the electrodes will have radioactivity about 4,000 times less than the least dangerous radioactive waste.